This invention relates to vehicle shock absorbers which are typically mounted between the wheels and chassis or body of an automobile, truck, motorcycle, etc. The invention relates to a shock absorber with damping characteristics that change depending upon the acceleration of parts of the shock absorber, most importantly, during downward acceleration of the vehicle wheel.
Shock absorbers which respond to accelerations of a vehicle wheel have demonstrated a remarkable ability to improve the performance of vehicles equipped with such shock absorbers. One such shock absorber has a movable inertia valve for opening a port during downward acceleration of the vehicle wheel. The acceleration sensitive shock absorber further includes means for biasing the inertia valve towards its open position in response to fluid flow through the shock absorber.
It is desirable to apply an upwardly directed spring load to the inertia valve in the shock absorber to reduce the effects of gravity. Ideally, the inertia valve is a pure inertial element unaffected by gravity. As the inertia valve approaches a weightless condition, the more sensitive it becomes to acceleration inputs and premature opening. A "weightless" inertia valve also becomes sensitive to pressure differentials during non-inertia valve extension events or body motion events. Body motion events create high pressure inside the piston as fluid is metered through the body motion valving.
Some inconsistency in performance was noted in mass produced shock absorbers. It was deduced, that sometimes the inertia valve would open in absence of a downward acceleration of the vehicle wheel. The inertia valve might open due to a body motion rather than a wheel motion. Opening of the inertia valve leads to a reduction in damping force when high forces are necessary to control vehicle body motions. Conversely, it might occur that the inertia valve did not open properly upon downward wheel acceleration.
It is desirable that the inertia valve should consistently open when it should, and should remain closed when it should not be opening. It is desirable to modify the structure only slightly to alleviate such inconsistencies in mass produced shock absorbers.